Hardy was born in Nottingham, the son of Richard Hardy, an architect, and his wife, Elizabeth Hannah Clavering.[2] He was educated not far away at Oundle School. He had intended to go to Oxford University in 1914, but on the outbreak of war he instead volunteered for the army, and was made a camoufleur, a camouflage officer. Hardy wrote that he had been[3]

equally drawn to science and art, and if the truth be known, I must confess that it is the latter that has the greater appeal. I am lucky in not having been torn between the two; I have managed to combine them.[3]

He was selected for camouflage work by the artist Solomon J. Solomon, who apparently mistook him for a different Hardy who was a professional artist.[4] Hardy however did have sufficient artistic skill to serve his military and scientific work. He illustrated his New Naturalist books with his own line drawings, maps, diagrams, photographs, and paintings.[5] For example, plate 2 of Fish and Fisheries illustrates the depicted "Rare and Unusual Fish in British Waters" both accurately and vividly. Hardy described the camoufleurs as including artists and "scientists with artistic inclinations", himself perhaps among them.[4]

Hardy was the zoologist on the RRS Discovery voyage to explore the Antarctic between 1925 and 1927, as part of the Discovery Investigations. Through his studies of zooplankton and its relationship with predators, he became expert in marine mammals such as whales. Whilst on board the Discovery he designed and later built a mechanism called the Continuous Plankton Recorder or CPR. The CPR collects plankton samples and stores them on a moving band of silk, preserving them in formalin. His pioneering research into plankton distribution and abundance is continued by the Sir Alister Hardy Foundation for Ocean Science (SAHFOS).

Hardy discussed his evolutionary ideas in his book The Living Stream (1965). He had written a chapter titled "Biology and Telepathy" where he explained that "something akin to telepathy might possibly influence the process of evolution". Evolutionary biologist Ernst Mayr described his views on evolution as a form of vitalism.[9] Hardy also suggested that certain animals share a "group mind" which he described as "a sort of psychic blueprint between members of a species." He also speculated that all species might be linked in a "cosmic mind" capable of carrying evolutionary information through space and time.[10]

In 1930, while reading Wood Jones' Man's Place among the Mammals, which included the question of why humans, unlike all other land mammals, had fat attached to their skin, Hardy realized that this trait sounded like the blubber of marine mammals, and began to suspect that humans had ancestors that were more aquatic than previously imagined. Fearing a backlash against such a radical idea, he kept this hypothesis secret until 1960, when he spoke, and later wrote, on the subject, which subsequently became known as the aquatic ape hypothesis in academic circles.

^Hardy's contribution to the scientific study of religion is reviewed in David Hay's book Something There: The Biology of the Human Spirit published in London in July 2006 by Darton, Longman & Todd and in the United States by Templeton Press in 2007.